#1235 Comparative effect on bone remodeling and inflammation biomarkers of citrate dialysate and bicarbonate dialysate in HDF-OL patients

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Abstract Background and Aims Hemodialysis (HD) treatment increases the inflammatory state of chronic kidney disease (CKD), which is associated with dysregulation of mineral bone metabolism. Reduced inflammation and increased bone formation have been described in Hemodiafiltration (HDF) compared with conventional HD. On the other hand, HD and OL-HDF using citrate-enriched dialysate are known to be safe and anti-inflammatory. However, the effects of post-dilution OL-HDF with citrate dialysate compared to bicarbonate dialysate on biomarkers of bone formation and resorption have not been studied. We aimed to compare the effect of bone remodeling markers and inflammation of different dialysates (citrate vs bicarbonate) in post dilution OL- HDF treatment. Method A total of 33 patients on conventional HD with bicarbonate citrate were included. At month 1, 18 patients, who did not require individualized adjustment of the dialysate composition such as potassium, were changed to HD with citrate dialysate and 15 patients remained with bicarbonate dialysate. By the second month, however, all patients were on OL-HDF with no change in buffer dialysate. Pre-dialysis blood samples were taken in both treatment groups at baseline (prior to the initiation of citrate dialysate in 18 patients), and at the first, second and fifth months after the introduction of citrate. Measurements of mineral homeostasis (calcium, phosphate, magnesium, parathyroid hormone, intact parathyroid hormone), inflammation (interleukin-6, β2-microglobulin, C-reactive protein) and bone remodeling markers (carboxy-terminal crosslinked telopeptide of type 1 collagen (CTX), as a biomarker of bone resorption and procollagen type 1 N-terminal pro-peptide (P1NP), as a biomarker of bone formation) were performed. All samples were collected before a mid-week dialysis session. Mineral homeostasis measurements were also performed before and after HD at the first and second month of the switch to citrate dialysate. Normally distributed data were presented as mean (standard deviation, SD) and median (interquartile range). Intra-subjects comparisons were analyzed using paired sample t-test or Wilcoxon signed-rank test. Comparisons between groups were analyzed using Mann-Whitney U test. Statistical analyses were performed using the SPSS (version 15.0, Chicago, IL, USA). p-value < 0.05. Results Overall, 75.7% (n = 25) of the subjects were male, the median age was 69 years (SD: 12) and 39.3% suffered diabetes (n = 13). Patients on citrate and bicarbonate dialysates were comparable for age, sex, comorbidities, months on dialysis and anemia control. Baseline mineral, bone remodeling and inflammation markers before HD, were also comparable in both groups. Only patients on bicarbonate dialysate had higher β2-microglobulin levels at baseline. Changes in serum levels of mineral, bone remodeling and inflammatory biomarkers at 5 months compared to baseline for both groups are shown in Table 1. After 5 months of follow-up, a 22% trend-reduction (p = 0.08) in P1NP as bone formation biomarker was observed in patients on citrate dialysate compared to those on bicarbonate dialysate. In addition, the fold change observed in CTX as parameter of bone resorption was attenuated in the citrate dialysate group (11% vs 116% in the bicarbonate dialysate group, p < 0.001). β2-microglobulin levels decreased significantly in both groups at 5 months but It is explained by the known effect of OL-HDF treatment on the inflammatory state of dialysis patients. Conclusion In patients on OL-HDF treatment the use of the citrate as dialysate may provide a benefit in bone remodeling by reducing bone resorption and trend to balance the bone formation/resorption. However, our results are in line with previous studies, where caution should be adopted in patients with very high parathyroid hormone levels, as this may be enhanced by reduced mineral turnover.